Personal defense weapon

Personal defense weapons (PDWs) are a class of compact, magazine-fed automatic firearms that are typically submachine guns designed to fire rifle-like cartridges. Most PDWs fire a small-caliber (generally less than 8 mm or 0.31 in in bullet diameter), high-velocity centerfire bottleneck cartridge resembling a scaled-down intermediate cartridge, essentially making them an "in-between" hybrid between a submachine gun and a conventional carbine.

The use of these rifle-like cartridges gives the PDWs much better ballistic performance (effective range, external ballistics and armor-penetrating capability) than conventional submachine guns, which fire larger-caliber but slower and less aerodynamic handgun cartridges. The low recoil of these "sub-intermediate" cartridges also makes muzzle jumps on PDWs (which typically have short barrels) much easier to handle than short-barreled rifles, especially when shooting in automatic fire or burst fire.

The name describes the weapon's original conceptual role: as a compact but powerful small arm that can be conveniently carried for personal defense, usually by support personnel behind the front line such as military engineers, logistic drivers, medical specialists, artillery crews, or signallers. These "second-line" personnel are not strictly combat troops expected to directly engage the enemy, but may still be at risk of encountering decently equipped (and often well-armored) hostile skirmishers and infiltrators, therefore having to defend themselves in close quarters. Such encounters will warrant an effective weapon that is easy to use while having sufficient firepower to suppress enemy charges and hold them beyond a safe perimeter to prevent the defenders from being overrun, but the risk of hostility is rare enough that a standard service rifle would be an unnecessary burden during their normal duties.

Because of their light weight, controllability, ease of operation and close-range effectiveness (can defeat a NATO CRISAT vest^[1] or an NIJ IIIA soft Kevlar armor^[2][3] at up to 200 m (220 yd)), PDWs have also been used by special forces, paramilitaries, heavily armed tactical police, and bodyguards.